The invention relates generally to disk drive spindle motors and, more particularly, to air bearings for use in connection with disk drive spindle motors.
A disk drive is a data storage device that stores information within one or more tracks of a disk shaped data storage medium (i.e., a disk). The data is read from the disk by spinning the disk about an axis of rotation while directing a transducer toward the area of the disk having the desired data. The transducer senses the desired data from the disk and generates an analog read signal in response thereto. The analog read signal is then converted into a digital format for use by a host computer coupled to the disk drive.
A typical disk drive includes one or more disks that are mechanically coupled to a hub. The hub, in turn, is coupled to a spin motor which provides the rotational forces necessary for imparting motion to the hub and the disk(s). To reduce friction in the disk drive and enhance stable rotation of the hub, among other things, any of various bearing structures can be used at the bearing between the moving and stationary portions of the disk drive. Structures that provide bearing support in a direction parallel to the axis of rotation are known as thrust bearings and structures that provide bearing support in a radial direction with respect to the axis of rotation are known as journal bearings. Historically, hardened spherical balls (i.e., ball bearings) have been used to reduce friction in both of these directions. More recently, however, air bearings have become popular for achieving bearing stability and reduced friction in disk drives.
Air bearings rely upon self-generated pressurized air in the bearing region to prevent contact between the bearing surfaces during disk rotation. As such, air bearings normally generate significantly less friction during full speed disk operation than do ball bearings. In addition, air bearings eliminate ball and race defects which cause non-repeatable runout. This results in less non-repeatable spindle run out and, correspondingly, less transducer position error. By decreasing position error, air bearing use effectively increases the density with which data can be stored on the disk in the radial direction.
A problem with air bearings occurs when the disk is just beginning to rotate. That is, before the disk reaches a threshold rotational velocity, the air pressure in the bearing region is low and is thus not capable of adequately supporting the rotating portion of the drive. The air bearing surfaces of the thrust bearing, therefore, come in contact with one another during these periods on non-rotation or low speed rotation. In addition, when the disk is at rest, the air bearing surfaces of the thrust bearing can stick together in a phenomenon known as xe2x80x9cjo-blockingxe2x80x9d or xe2x80x9cstictionxe2x80x9d. This xe2x80x9cstictionxe2x80x9d between bearing surfaces must be overcome by the spin motor before the disk can spin up and, therefore, can place a large load on the spin motor during disk drive initialization. This increased load on the spin motor can contribute to a shortened life span for the motor. In addition, friction between the air bearing surfaces during spin up and spin down can generate wear particles that become trapped in the bearing area during operation. If these wear particles are allowed to build up, they can eventually compromise the operation of the bearing and could possibly lead to bearing seize up.
Therefore, there is a need for an air bearing structure for use in a disk drive that produces relatively little stiction during an initial disk spin-up period. In addition, there is a need for an air bearing structure that is capable of reducing the generation and collection of wear particles in the bearing area.
The present invention relates to an air bearing structure for use in a disk drive device that produces relatively little stiction between air bearing surfaces during an initial disk spin up period. In general, the structures of the present invention are designed to minimize contact between the air bearing surfaces of the bearing when the hub of the disk drive is at rest or rotating below a threshold velocity. This minimization of contact is accomplished with relatively little effect on the performance of the air bearing. The inventive structures also provide for a significant reduction in the collection of wear particles in the air bearing region. The principles of the present invention can be used in virtually any form of disk drive device, including magnetic disk drives, optical drives, and other data storage devices utilizing a disk shaped medium.
In accordance with the present invention, reduced contact between thrust bearing surfaces is achieved by appropriately shaping the bearing surfaces. Air bearings of the past typically parallel thrust bearing surfaces in the air bearing region to achieve the necessary lift. Consequently, the gap height of these prior thrust bearings is constant as a function of radial distance from the axis of rotation. In accordance with the present invention, the bearing surfaces of the thrust bearing are shaped such that the height of the gap between the bearing surfaces varies as a function of radial distance. This non-uniform gap height exists while the disk is at rest and also when the disk is rotating at full operational speed (and at all speeds in between). Therefore, contact between the air bearing surfaces during reduced velocity operation is limited to a small portion of the overall surface areas of the air bearing surfaces. The reduced contact area also generates considerably less stiction on subsequent spin up of the disk than would a parallel plate configuration.
Various bearing surface shaping techniques are provided in accordance with the present invention. In one approach, one or both of the air bearing surfaces in the thrust bearing are xe2x80x9ccrownedxe2x80x9d (i.e., given the shape of a section of a sphere surface). In another approach, stepped or sloped bearing surfaces are used. In yet another approach, sacrificial plating is used to achieve a non-uniform gap height in the radial direction. That is, one or both of the air bearing surfaces within the thrust bearing are plated over a portion of their total areas so that only the plated portion of the surface contacts the opposing air bearing surface when the disk is at rest. In a preferred implementation of the sacrificial plating approach, the plating is arranged in a ring configuration on the air bearing surface. The sacrificial plating is preferably formed using a material that is softer than the material used for the air bearing surfaces themselves.
In another aspect of the present invention, structures are provided for preventing the collection of friction generated wear material in the thrust bearing region. More specifically, groove patterns are provided for use in the thrust bearing that pump air radially outward over most or all of the thrust bearing region. These outward air currents tend to blow any wear particles within the bearing region outward toward the outer diameter of the bearing. wear particle collection functionality is also provided for collecting the wear particles after they have been ejected from the thrust bearing. In one embodiment, for example, a cavity is provided for catching the ejected wear particles. In another embodiment, an adhesive and/or magnetic material is provided for holding the particles after they have been ejected. By capturing the ejected particles after they have been blown from the bearing, the particles are prevented from making their way to other areas of the disk drive where they can have a negative impact on disk drive performance.